A variety of methods are known in the food preparation art for preparing snack foods such as potato chips and other forms of vegetable and grain chips such as corn or tortilla chips. Most of these methods, however, rely on cooking techniques in which the potato or other chip is immersed in a reservoir of hot oil for a period of time. Known as "deep fat" frying, the effect of this cooking process is to substantially reduce the water content of the potato slice while allowing some fat uptake. The moisture content of fresh potato slices is typically about 85% of the weight of the slice while "deep fat" fried potato chips commonly have a moisture content of less than 5% by weight. The deep fat frying process, however, also typically results in a finished potato chip having a fat content from about 30% to about 45% of the total weight of the finished chip.
The high fat content of conventionally prepared potato chips is considered undesirable by many people because of the increased caloric value and the relatively short shelf life of the resulting chip. The fat stored in a potato chip can become rancid after long term storage, imparting an undesirable odor and taste to the chip. A number of cooking methods have been developed in the past to reduce the fat content of potato chips and the like. U.S. Pat. No. 3,365,301 to Lipoma et al., for example, discloses a process for making fried chips by partially cooking potato slices in an oil bath at higher temperatures and for shorter periods of time than normally used in conventional oil immersion cooking processes, with a final cooking step employing electromagnetic heating, such as microwave heating. The higher temperature and shorter time period of the oil immersion portion of the Lipoma cooking process is believed to result in a final chip having a reduced fat content. This approach, however, does not eliminate the uptake of fat by the chip during the first step of the cooking process. Another approach, disclosed in U.S. Pat. No. 4,283,425 to Yuan et al., is to prepare potato chips by coating a raw potato slice with globular proteins and an optional layer of edible oil on top of the protein coating. The potato slice prepared in this fashion is then cooked by microwave heating. While eliminating the step of deep fat frying, the Yuan approach still produces a potato chip having an exterior coating of at least globular proteins. At column 3, lines 47-59 the Yuen patent states the protein coating is an essential element in successfully microwaving the potato slices. Use of microwave heating alone to prepare potato chips has previously been considered unsuitable because of gelatinization, a tendency of starches in the potato slice to coat the exterior surfaces of the slice and to form a gummy seal which hardens with further heating. The Yuen patent, for example, notes at column 2, lines 45-50 that efforts to remove more than 3% of the moisture content of a potato slice by microwave heating causes starch gelatinization.
Thus, there still exists a need for a method of preparing potato and like vegetable chips, as well as corn, tortilla and other grain chips, having both the taste and consistency of the widely known and broadly appreciated deep fat fried potato, corn and tortilla chips, but which are fat free or virtually fat free.